FIG. 1 shows a non-roaming 3GPP network architecture for EPS.
A User Equipment (UE) may interact with EPS using the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) radio access. UE-related control signalling is handled by Mobility Management Entity (MME) with support of subscription information provided by the Home Subscriber Server (HSS). User payload is handled by the Serving Gateway (S-GW) and the PDN Gateway (P-GW). The P-GW may interact with a Policy and Charging Rules Function (PCRF).
The 3GPP network may be organized using multiple MMEs serving the same tracking areas of an LTE radio network and multiple SGSNs serving the same routing areas of a GERAN/UTRAN radio network. These architecture options are named MME Pool and SGSN Pool respectively.
FIG. 2 shows an example of MME pool-area configuration. An SGSN pool-area configuration may be provided having a similar architecture.
Concerning legacy mechanisms at MME Restoration, the SGSN/MME shall according to present standards delete all UE contexts affected by the restart that it may have stored. For UE contexts not affected by the restart, the SGSN/MME shall update HSS at a next UE-originated event. After restart, an SGSN/MME changes the restart counter in GTP signalling with the SGW. An SGW that receives a change in the restart counter may select to remove all UE contexts related to the restarted SGSN/MME, or, select to use Network triggered service restoration procedure.
For a detected communication failure at interface S4 or S11, a SGSN/MME shall according to standards delete all PDP (Packet Data Protocol) contexts/PDN connections that are affected by the communication failure. An SGW that detects a communication error may select to remove all UE contexts related to the restarted SGSN/MME, or, select to use Network triggered service restoration procedure.
Based on 3GPP TS 23.007 section 25, the SGW may as an option support the network triggered service restoration procedure. After a restart of the SGSN/MME and when the SGW detects a change in restart counter, it removes bearers that are not allowed to be active when the UE is in idle state but does not remove the UE context. The SGW does at the same time start a timer to supervise that remaining UE contexts are not kept handled indefinitely by the node.
3GPP TS 29.274 provides a protocol specification of the Evolved GPRS Tunneling Protocol (GTP) for Control plane. Some protocol uses are application signaling between MME and S-GW at the S11 interface, and application signaling between S-GW and P-GW at the S5 and S8 interfaces.
3GPP TS 29.060 provides a protocol specification of the GPRS Tunneling Protocol (GTP) across the Gn and Gp interface.
At a received downlink packet with user plane data at S5/S8, the SGW shall immediately send a Downlink Data Notification message including IMSI to the SGSN/MME. The SGW may select to send the Downlink Data Notification including IMSI to a different SGSN/MME in a serving SGSN Pool/MME Pool.